HER2-positive breast cancers make too much of the HER2 protein. The HER2 protein sits on the surface of cancer cells and receives signals that tell the cancer to grow and spread. About one out of every four breast cancers is HER2-positive. HER2-positive breast cancers tend to be more aggressive and harder to treat than HER2-negative breast cancers.

Herceptin works by attaching to the HER2 protein and blocking it from receiving growth signals. Herceptin, which is given intravenously, is approved by the U.S. Food and Drug Administration to:

treat advanced-stage, HER2-positive breast cancers

lower the risk of recurrence (the cancer coming back) of early-stage, HER2-positive breast cancers with a high risk of recurrence

Herceptin is often given at the same time as or right after chemotherapy. In many cases, the chemotherapy regimen may include an anthracycline.

Anthracycline chemotherapy medicines are:

Adriamycin (chemical name: doxorubicin)

Ellence (chemical name: epirubicin)

Doxil (chemical name: liposomal doxorubicin)

daunorubicin (brand names: Cerubidine, DaunoXome)

mitoxantrone (brand name: Novantrone)

Anthracyclines work by damaging cancer cells’ genes and interfering with their reproduction. Anthracyclines also can cause heart problems.

To do the study, the researchers looked at the medical records of 23,006 women diagnosed with breast cancer between 2006 and 2009:

more than 62% of the women were between 45 and 64 years old

2,850 of the women were treated with Herceptin

The women were followed until the end of 2013.

To compare the effects of Herceptin, the researchers also analyzed the records of two smaller groups of women: one treated with Herceptin and one not treated with Herceptin. These women had similar characteristics (age, other treatments, other health conditions):

1,051 women were treated with Herceptin, of these women 661 also were treated with an anthracycline

3,794 women were not treated with Herceptin

Overall, more of the women treated with Herceptin had heart problems compared to women who were not treated with Herceptin:

4.03% of women treated with Herceptin had heart problems

2.88% of women not treated with Herceptin had heart problems

After adjusting for other factors that may affect a woman’s risk of having heart problems, such as her age, other health problems, and other treatments:

2.85% of women treated with Herceptin had heart problems

1.68% of women not treated with Herceptin had heart problems

during the 4 years of follow-up.

In the smaller groups of women, Herceptin increased the risk of heart problems in the first year of treatment. This risk seemed to gradually decrease after the first year.

Compared with results from other studies that included mainly white women, the rate of heart problems in Taiwanese women in the study is about 5 times lower.

The results raise a question: Are differences in heart problem risk factors, such as age, anthracycline treatment, and other health conditions that affect the heart, such as high blood pressure, responsible for the lower number of heart problems in Asian women treated with Herceptin? Or is the risk of heart problems really lower among Asian women?

When the researchers compared their results with a study done in the United States and adjusted for risk factors that affect heart problems, they found that the rate of heart problems was lower in the Asian women in this study across all treatment groups. This suggests that the risk factors are not the sole reason for the difference.

While the results of this study are encouraging, more research is needed to determine exactly why Asian women seem to have a lower rate of heart problems when treated with Herceptin.

If you’ve been diagnosed with HER2-positive breast cancer and Herceptin and/or anthracycline chemotherapy will be part of your treatment plan, it’s a good idea to ask your doctor about your personal risk of treatment-related heart problems and whether visiting a cardiologist before treatment starts is a good idea for you, no matter your ethnicity or age. The cardiologist can evaluate your heart function and decide if you’re at risk of developing heart disease or heart failure from breast cancer treatment. You also may want to ask your oncologist how your heart function will be monitored during treatment.

Together, you can decide on the best treatment plan for your unique situation.